1. Field of the Invention
The present invention relates to a wrench with a fixed maximum operational torque to prevent damage to the object secured by a fastener driven by the wrench.
2. Description of the Related Art
FIG. 8A of the drawings illustrates a conventional wrench 1 having a hexagonal driving portion with six planar faces 2 for engaging with six faces of a hexagonal groove in a top face of a fastener. However, slide tends to occur between the planar faces of the driving portion of the wrench 1 and the faces of the fastener. FIG. 8B illustrates a so-called TROX wrench 3 having plural arcuate faces 4 for engaging with corresponding arcuate faces in a top face of a fastener. Such a TROX wrench 3 is used to tighten important parts of a car and cutting tools. As illustrated in FIG. 9, a blade 7 is tightened to a cutting tool 5 by a bolt 6. However, the expensive blade 7 tends to be damaged when the bolt 6 is excessively tightened. But the blade 7 could fly away and thus cause injury if the bolt 6 is not tightened to the desired extent.
An object of the present invention is to provide a wrench with a fixed maximum operational torque such that when the torque applied by the user is greater than the maximum operational torque, the wrench slides and the fastener is not turned. Thus, damage to the object secured by the fastener resulting from over-tightening is prevented.
Another object of the present invention is to provide a wrench with a fixed maximum operational torque that can be altered in response to the actual use.
A wrench in accordance with the present invention comprises a substantially L-shaped rod and a casing. The L-shaped rod comprises a first section and a second section, a driving portion being formed on the second section for engaging with a fastener. The casing includes a receiving section for accommodating the first section of the rod and a positioning hole for rotatably receiving a portion of the second section of the rod. The receiving section of the casing is configured to allow relative pivotal movement between the casing and the rod. The casing further includes a receptacle that preferably extends along an axis offset from a longitudinal axis of the first section of the rod. An engaging member is mounted in the receptacle of the casing and biased to press against the first section of the rod, thereby exerting an engaging force between the first section of the rod and the engaging member. When a rotational force applied to the casing is smaller than the engaging force, the rod is turned to thereby turn the fastener. When a rotational force applied to the casing is greater than the engaging force, the casing slides while the rod is not turned.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.